Abstracts

Rationale: Previous studies on language localization in healthy and diseased brain have demonstrated that neurological disorders such as brain tumors, stroke, and epilepsy can cause significant alterations in lateralization and localization of the language-specific areas [1]. Functional magnetic resonance imaging (fMRI) studies in adults with left epileptogenic areas near language cortex have been showed that their language representation is more atypical (right sided or bilateral) in comparison to those with right seizure focus [1,2]. Furthermore, it has been found that early onset seizures originating in the left hemisphere can lead to language reorganization toward the right hemisphere [1,3]. In this study, fMRI data collected from patients with epilepsy during a language task. We investigated language lateralization of patients with left and right epileptogenic areas using the lateralization index (LI). In addition, the correlation between LI and early seizure onset age was investigated. Methods: Seventeen patients with epilepsy were selected from phase I epilepsy surgery evaluation at Le Bonheur Children’s Hospital. The seizure focus in 11 patients (average age 11.3) was in the left hemisphere, and the seizure focus in six patients (average age 12.7) was in the right hemisphere. The fMRI data were collected while patients performed a sentence completion task. We used a 4-minute block design paradigm with 15 seconds alternation between rest and activation. For computing language lateralization index, the LI toolbox implemented in SPM8 was used [4]. The LI toolbox identifies activate voxels for a set of ROIs based on adaptive thresholding method and computes the laterality as LI = (Leftactivation – Rightactivation) / (Leftactivation + Rightactivation). Results: Mean and standard deviation of the LI for patients with left and right hemisphere epilepsy focus were 0.17± 0.2 and 0.31 ± 0.15, respectively. As expected, the LI in patients with left hemisphere epilepsy focus was less than those with right hemisphere epilepsy focus. However, we were not able to find a significant difference between two groups (p = 0.72). Furthermore, the LI and seizure onset age were correlated in patients with right hemisphere epilepsy (r = 0.83, p = .04) but not in patients with left hemisphere epilepsy (r = 0.11, p = 0.75). Conclusions: The likelihood of having atypical language lateralization is higher in patients with left hemisphere epilepsy. Additionally, we found that early onset seizures in the right hemisphere can lead to more left lateralized language-specific areas. Funding: This study was funded by the Children’s Foundation Research Institute, Memphis, TN.